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Message-Id: <20200723171227.446711-4-mic@digikod.net>
Date: Thu, 23 Jul 2020 19:12:23 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Mickaël Salaün <mic@...ikod.net>,
Aleksa Sarai <cyphar@...har.com>,
Alexei Starovoitov <ast@...nel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Christian Brauner <christian.brauner@...ntu.com>,
Christian Heimes <christian@...hon.org>,
Daniel Borkmann <daniel@...earbox.net>,
Deven Bowers <deven.desai@...ux.microsoft.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Biggers <ebiggers@...nel.org>,
Eric Chiang <ericchiang@...gle.com>,
Florian Weimer <fweimer@...hat.com>,
James Morris <jmorris@...ei.org>,
Jan Kara <jack@...e.cz>,
Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
Matthew Garrett <mjg59@...gle.com>,
Matthew Wilcox <willy@...radead.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Mimi Zohar <zohar@...ux.ibm.com>,
Philippe Trébuchet <philippe.trebuchet@....gouv.fr>,
Scott Shell <scottsh@...rosoft.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Shuah Khan <shuah@...nel.org>,
Steve Dower <steve.dower@...hon.org>,
Steve Grubb <sgrubb@...hat.com>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
Thibaut Sautereau <thibaut.sautereau@...p-os.org>,
Vincent Strubel <vincent.strubel@....gouv.fr>,
kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: [PATCH v7 3/7] exec: Move path_noexec() check earlier
From: Kees Cook <keescook@...omium.org>
The path_noexec() check, like the regular file check, was happening too
late, letting LSMs see impossible execve()s. Check it earlier as well
in may_open() and collect the redundant fs/exec.c path_noexec() test
under the same robustness comment as the S_ISREG() check.
My notes on the call path, and related arguments, checks, etc:
do_open_execat()
struct open_flags open_exec_flags = {
.open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
.acc_mode = MAY_EXEC,
...
do_filp_open(dfd, filename, open_flags)
path_openat(nameidata, open_flags, flags)
file = alloc_empty_file(open_flags, current_cred());
do_open(nameidata, file, open_flags)
may_open(path, acc_mode, open_flag)
/* new location of MAY_EXEC vs path_noexec() test */
inode_permission(inode, MAY_OPEN | acc_mode)
security_inode_permission(inode, acc_mode)
vfs_open(path, file)
do_dentry_open(file, path->dentry->d_inode, open)
security_file_open(f)
open()
/* old location of path_noexec() test */
Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Signed-off-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20200605160013.3954297-4-keescook@chromium.org
---
fs/exec.c | 12 ++++--------
fs/namei.c | 4 ++++
2 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index bdc6a6eb5dce..4eea20c27b01 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -147,10 +147,8 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
* and check again at the very end too.
*/
error = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
- goto exit;
-
- if (path_noexec(&file->f_path))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ path_noexec(&file->f_path)))
goto exit;
fsnotify_open(file);
@@ -897,10 +895,8 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
* and check again at the very end too.
*/
err = -EACCES;
- if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
- goto exit;
-
- if (path_noexec(&file->f_path))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
+ path_noexec(&file->f_path)))
goto exit;
err = deny_write_access(file);
diff --git a/fs/namei.c b/fs/namei.c
index a559ad943970..ddc9b25540fe 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2863,6 +2863,10 @@ static int may_open(const struct path *path, int acc_mode, int flag)
return -EACCES;
flag &= ~O_TRUNC;
break;
+ case S_IFREG:
+ if ((acc_mode & MAY_EXEC) && path_noexec(path))
+ return -EACCES;
+ break;
}
error = inode_permission(inode, MAY_OPEN | acc_mode);
--
2.27.0
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